Measurement using a sophisticated biomolecule identification function such as an antigen-antibody reaction and binding of a DNA fragment (DNA probe) to DNA is becoming an important technique in clinical testing, measurement in the field of biochemistry, and measurement for environmental pollutants. Examples of the measurement are micro-TAS (Total Analysis Systems), micro combinatorial chemistry, chemical IC, chemical sensor, biosensor, microanalysis, electrochemical analysis, QCM measurement, SPR measurement, and ATR measurement. In the field of measurement, the amount of sample solution to be measured is often very small.
In this measurement, a small amount of sample solution is directly transferred to a detecting portion to measure it with high sensitivity and high efficiency without decreasing the concentration of the analyte. As a technique for transferring a small amount of sample solution, a several hundred μm-wide fluidic channel is formed on a substrate, and a solution is transferred by an external pressure by a syringe pump or the like. Alternatively, a solution is transferred by electrostatic force, by electrowetting, by changing the volume or generating bubbles upon heating, or by using an electroosmotic flow.
To transfer a small amount of sample solution by these methods, it is necessary to form a microchannel as a fluidic channel on a substrate (chip), and arrange other components on this substrate. It is not easy to fabricate this structure. Transferring a sample solution by an external pressure requires components such as a pump and tube in addition to a chip which forms a fluidic channel. A sample solution is wasted on the transfer path including the tube, which exerts a limitation on decreasing the amount of sample solution.
As a method of analyzing a small amount of sample solution, paper chromatography analysis using filter paper has conventionally been known. For example, improved immunochromatography and immunoconcentration have been proposed as simple, low-cost means for measurement of biological substances (reference 1: Japanese Patent Publication No. 7-036017, and reference 2: Japanese Patent Laid-Open No. 2000-329766). There is also proposed a measurement chip in which filter paper is arranged in a fluidic channel formed in a plastic structure (reference 3: Amal. Chem. 2005, 77. 7901-7907). However, these paper chromatography methods have limitations in the shape of the fluidic channel and the like, and cannot perform complicated chemical analysis.
Under the circumstance, it is recently proposed to form, on or in a substrate by a microfabrication technique, regions serving as a fluidic channel and pump for transferring a sample solution by capillary action (reference 4: Martin Zimmermann, Heinz Schmid, Patrick Hunziker and Emmanuel Delamarche, “Capillary pumps for autonomous capillary systems”, The Royal Society of Chemistry 2007, Lab Chip, 2007, 7, 119-125, First published as an Advance Article on the web 17 Oct. 2006). A measurement chip fabricated by this technique has an inlet port for introducing a sample solution, a capillary pump for sucking it, and a measurement fluidic channel formed between the inlet port and the capillary pump. The capillary pump is formed from a cavity containing a plurality of pillars which connect the ceiling and bottom. The pillars have an interval enough to cause capillary action. In this measurement chip, when a sample solution is introduced from the inlet port, it sequentially flows from the inlet port to the measurement fluidic channel and pump. When the sample solution reaches the capillary pump, it is sucked by the capillary action of the capillary pump. The sample solution which stays at the inlet port flows to the pump through the measurement fluidic channel by the suction force of the capillary pump.